This invention pertains to homogenous nuclear reactor control systems and more particularly to a system for varying the amount of boron in the coolant fluid for a nuclear reactor system.
The presently utilized system for changing the boric acid concentration in the coolant fluid of a nuclear reactor system generally accomplishes same by drawing off a portion of the coolant and replacing that portion with an equivalent amount of either demineralized and deaerated water, or water which has been previously blended so as to have a high concentration of boric acid.
In general, the coolant removed from the coolant system of a nuclear reactor plant is first conveyed to an evaporator which concentrates the boric acid to a fixed amount or percentage by weight of boron and stores this concentrated boric acid solution in one tank and the generally demineralized and deaerated water from the evaporator in another tank. The two storage tanks might then be used to feed either demineralized and deaerated water or to mix the highly concentrated boric acid concentrate with water so as to vary the boration of the solution fed to the nuclear reactor.
More recently, the use of anion exchange beds containing basic anion resins which operate to directly change the boric acid in the primary coolant stream, depending upon the temperature of the influent to such a bed, have been contemplated for this purpose. Such a system is shown and described in U.S. Pat. No. 3,666,626 - Gramer et al entitled "Method and Means for Reversibly Changing the Boric Acid Concentration in the Coolant of a Nuclear Reactor" assigned to the same assignee as the invention. In accordance with that invention, the enrichment or depletion of boric acid in the primary coolant water is accomplished by passing a portion of that coolant through an anion exchange resin bed charged with boric acid. The temperature of the water flowing through the bed is varied such that boric acid enters the coolant at relatively higher temperatures and is taken from the coolant and stored in the resin bed at relatively lower temperatures.
Each of the above systems has inherent advantages and disadvantages. For example, the evaporative recycle system is capable of concentrating a great amount of boric acid and storing same. However, if it must perform this function rapidly, the evaporator and associated equipment becomes exceedingly large and expensive. On the other hand, the ion exchangers can perform the function of rapidly varying the quantity of borate ions in the primary coolant of the reactor system. However, the storage capacity of the ion exchangers is rather limited unless the ion exchange tanks are made exceedingly large or numerous and such a large quantity of resin is used so as to make the system prohibitively expensive.
Further, ion exchange beds of the prior art have been contemplated for use simultaneously while either connected in series or in parallel. Thus all of the ion exchangers would handle an equal portion of the total required concentration change. It is now known that the storage capacity of a resin bed is lower for lower concentrations of borate ions in the flow passing therethrough. Accordingly, the simultaneous use of a plurality of ion exchangers necessitates an amount of resin in excess of that which might be used when the variation in storage capacity with concentration is taken into account.